Xylylene diisocyanate (hereinafter, referred to as XDI) is classified into aliphatic isocyanate, even though it contains an aromatic ring, and is a very useful compound as a raw material for polyurethane-based materials, polyurea-based materials, or polyisocyanurate-based materials in chemical, resin, and paint industries.
Commonly, aliphatic isocyanate is prepared by a phosgenation process of reacting a raw material amine with phosgene. For example, XDI is prepared by reacting xylylene diamine (hereinafter, referred to as XDA) with phosgene. However, a side reaction frequently occurs during phosgenation for the preparation of XDI, because of high reactivity of the amino group, similar to the characteristic of aliphatic isocyanate. Impurities generated by the side reaction affect a production reaction of a polyurethane resin to generate a problem of quality deterioration of the resin.
Therefore, many methods of preparing high-purity XDI by reducing the content of the generated impurities have been studied and proposed.
Specifically, Korean Patent Publication No. 1994-0001948 discloses a method for preparing high-purity XDI by using an ester-based compound such as amyl acetate or hexyl acetate as a reaction solvent during preparation of xylylene diisocyanate by reaction of xylylene diamine or a hydrochloride thereof with phosgene. However, this method is problematic in that the solvent is expensive and purity and yield are still low.
Korean Patent No. 0953019 discloses a method for preparing isocyanate by phosgenation of amine hydrochloride which is prepared by a salt-forming process of reacting a linear or cyclic aliphatic amine with hydrogen chloride, wherein a pressure is applied during the salt-forming process in order to solve the transfer problem of amine hydrochloride.
Further, as a non-phosgenation method of using no phosgene, Korean Patent No. 1318828 discloses a method for preparing xylylene diisocyanate through non-phosgenation, wherein a diamine compound is reacted with alkyl chloroformate or dialkyl carbonate to prepare biscarbamate, which is then subjected to decomposition, thereby degrading and removing alcohol having a relatively low boiling point. However, as compared with the phosgenation method, this method is disadvantageous in terms of cost, and its application to industrial mass-production is difficult.
U.S. Pat. No. 5,196,572 also discloses a method for preparing xylylene diisocyanate through decomposition of carbamate. However, as compared with the phosgenation method, this method is also disadvantageous in terms of cost, its application to industrial mass-production is difficult, and its yield and selectivity are very low.